Shutters with horizontal blades have been known for probably hundreds of years. Usually the blades are coupled to a pull bar or control bar so that the blades can be swung upwardly and downwardly between open and closed positions. In the past, when the blades were made of wood, simple wood fastenings such as screw eyelets could be secured in the edges of the blades and wire hooks could be secured in the pull bar which was also made of wood.
Many variations on this basic system are shown in earlier Patents.
More modern shutters of this type are made with blades of extruded plastic material. The material is hollow so that it presents a hollow aerofoil shape, and such shutter blades have a pleasing appearance. It is also desirable that the pull bar shall also be made of hollow plastic and that the attachments between the pull bar and blades shall also be made of plastic so that the entire shutter can be formed of plastic material giving it an extended working life without maintenance, and also reducing the cost.
The attachment of the pull bars to the blades requires that, at the point of attachment to each blade, the attachment device is secure and the blades shall be capable of rotational movement relative to the pull bar, in order to permit the blades to swing between open and closed positions.